Control method for engine thermal management

ABSTRACT

A control method for engine thermal management that provides an electronic fan clutch and an electronic water pump in cooperation with an operation of an electronic thermostat, thereby achieving efficient engine thermal management and reducing a loss of load. The control method includes the steps of obtaining an engine coolant temperature and engine driving information and calculating a required fan rotational speed based on the obtained current coolant temperature information and the obtained engine driving information. The method calculates a control value for controlling a rotational speed of a cooling fan and checks a current operating state of the electronic thermostat. The method determines whether to operate the electronic water pump and control the cooling fan rotational speed based on the checked current operating state of the electronic thermostat, and controls the electronic water pump and the electronic fan clutch of the cooling fan based on the determination result.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2015-0082418, filed on Jun. 11, 2015, the contents of which are incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to a control method for engine thermal management.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

In general, fuel efficiency of a vehicle may be improved by reducing driving loss of components that consume engine power.

Therefore, recently, an electronic control method is applied which is driven by receiving power from the engine through a pulley and a belt and may variably control operating states of the existing mechanical components that consume engine power.

As a representative component that consumes engine power, there may be an engine thermal management system, particularly, a cooling fan installed in a radiator and a water pump for pumping and circulating a coolant are among the components of an engine cooling device.

As the cooling device for engine thermal management, water-cooled cooling devices using a coolant are applied to the vehicle in most instances, and in the case of the water-cooled cooling device, the coolant is circulated in water jackets formed in a cylinder block and a cylinder head in order to cool the engine.

The water-cooled cooling device mainly includes a radiator and a cooling fan (radiator fan) which discharge heat of the coolant, which is transferred from the engine, to the outside, a coolant line which is configured to circulate the coolant between the engine and the radiator, a bypass line which bypasses the coolant to prevent the coolant from passing through the radiator, a thermostat which opens and closes a coolant line at the radiator side and the bypass line so as to allow the coolant to selectively pass through the radiator, and a water pump which pumps the coolant and circulates the coolant through the coolant line.

In this configuration, the coolant circulating along the coolant line passes through the radiator, and a cooling fan is mounted in the radiator to discharge heat of the coolant to the outside through air that flows in when the cooling fan is rotated.

The thermostat is a kind of three-way valve that adjusts a flow rate of the coolant flowing into the radiator in accordance with a coolant temperature or the like, and when the coolant temperature becomes equal to or higher than a predetermined temperature, the thermostat sends the coolant to the radiator to maintain the coolant temperature to an appropriate temperature.

The engine cooling device is a device to protect the engine, but engine power is consumed to operate the components of the cooling device.

In a case in which the coolant temperature (engine temperature) is excessively low (a state in which a temperature of oil that is a lubricant is low) in a section which the engine initially starts when the cooling device is applied, frictional loss of the engine is increased, which may cause a deterioration in fuel efficiency.

Therefore, the engine cooling device is controlled so as to maintain the coolant temperature, that is, the engine temperature to an appropriate temperature while the engine is being operated, reduce a heat loss by preserving heat of the engine in the section in which the engine initially starts, quickly warm up the engine, and reduce a frictional loss through early engine warming up.

Since the cooling fan and the water pump are components that consume engine power while being driven by receiving engine power through the pulley and the belt, it is desired to variably control rotational speeds of the cooling fan and the water pump in accordance with a coolant temperature and an engine driving condition in order to maintain the engine temperature to an appropriate temperature and minimize consumption of engine power.

A prior art mechanical water pump receives engine power through the pulley and the belt, and is always operated as the engine is operated even in a low-temperature and low-load region, in which it is not necessary to cool the engine, such that a loss of power occurs and it is difficult to reduce the time required to warm up the engine while the engine is idling after a cold start, and as a result, there is a problem in that fuel efficiency deteriorates because of a frictional loss.

In order to address the above concern, an electronic fan clutch (fluid type fan clutch which may be electronically controlled) has been used to intermittently provide engine power to the cooling fan and change the rotational speed.

Even in the case of the water pump, an electronic water pump (also called a clutch water pump) has been used in which an electronic clutch is applied as an intermittent mechanism for intermittently controlling engine power, thereby changing the rotational speed of the electronic water pump in accordance with a coolant temperature and an engine driving condition.

In a cooling fan system to which the electronic fan clutch is applied, an electronic control unit (hereinafter, referred to as an ‘ECU’) receives a coolant temperature detected by a coolant temperature sensor and a cooling fan rotational speed detected by a rotational speed sensor, and determines a target rotational speed according to the coolant temperature based on a map, and thereafter, the ECU outputs a valve control signal for performing proportional-integral (PI) control for a fan clutch by using the cooling fan rotational speed detected by the rotational speed sensor and the target rotational speed, thereby controlling the cooling fan rotational speed to the target rotational speed.

Since the electronic fan clutch is applied, it is possible to reduce engine power consumed by the cooling fan and time required to consume power, thereby improving fuel efficiency of the vehicle.

Related prior art relevant to the electronic fan clutch or a method of controlling the electronic fan clutch, there are Korean Patent No. 10-1459944 (Nov. 3, 2014), Korean Patent Application Laid-Open No. 10-2014-0075385 (Jun. 19, 2014), Korean Patent No. 10-1305399 (Sep. 2, 2013), and Korean Patent No. 10-1241212 (Mar. 4, 2013).

Related prior art relevant to the electronic water pump or a method of controlling the electronic water pump, there are Korean Patent Nos. 10-1459970 (Nov. 3, 2014) and 10-1049430 (Jul. 8, 2011).

In a system to which the electronic water pump is applied, the ECU controls the rotational speed of the water pump in accordance with a coolant temperature detected by the coolant temperature sensor and an engine load (engine torque) condition, and because magnetic force generated by a solenoid coil when electric power is applied is larger than a force of a spring, clutch attachment (clutch ON) occurs, such that the pulley and a pump shaft are connected so as to transmit power (flow rate: 100%, pulley rotational speed=pump shaft rotational speed).

In contrast, when electric power is not applied, a clutch disk returns to an original position by force of the spring (clutch OFF), and a gap is formed between the pulley and the disk, such that an induced magnetic field is generated between a permanent magnet and a cooling ring.

In this case, a slip occurs between the pulley and the disk of the water pump, and the rotational speed of the water pump is determined depending on an intensity of the magnetic field of the permanent magnet.

When the electronic water pump is applied, it is possible to reduce driving time of the water pump and consumption of engine power, thereby improving fuel efficiency of the vehicle, and reducing a frictional loss and improving fuel efficiency by quickly warming up the engine at the time of an initial cold start.

As an engine thermal management system, a general wax type mechanical thermostat, which opens and closes a flow path of a coolant line connected to the radiator in accordance with an engine coolant temperature, has been applied to the engine cooling device in the related art.

However, in a case in which the mechanical thermostat which opens and closes a coolant flow path only depending on the engine coolant temperature, is used, there is a limit in adjusting the coolant temperature (engine temperature) in accordance with an engine load, and it is difficult to control the coolant temperature to a high coolant temperature in a low-load region and to a low coolant temperature in a high-load region.

Therefore, in order to supplement the drawbacks of the mechanical thermostat, an electronic thermostat, which uses a controllable separate heat source and opens and closes a coolant flow path connected to the radiator in accordance with an engine load, a vehicle speed, and an atmospheric temperature as well as the coolant temperature, has been developed and applied.

Related prior art relevant to the electronic thermostat, there are Korean Patent No. 10-1416393 (Jul. 1, 2014), Korean Patent No, 10-1338468 (Dec. 2, 2013), Korean Patent Application Laid-Open No. 10-2013-0114505 (Oct. 17, 2013), and Korean Patent No. 10-1316879 (Oct. 2, 2013).

One prior art form of an electronic thermostat is configured so that an initial expansion temperature of a wax element is set to be high, and a heating element is mounted on the wax element to heat the wax element through the heating element, and as a result, it is possible to control an operating temperature separately from the coolant temperature by applying electric power to the heating element or cutting off the electric power.

In this case, as an example, it is possible to use a map in which operation ON/OFF regions of the electronic thermostat are set in accordance with the coolant temperature, the engine load, and the vehicle speed.

That is, by using the map, the ECU controls an operation of the heating element by applying or cutting off electric power in accordance with the coolant temperature, the engine load, and the vehicle speed, thereby maintaining an OFF state of the thermostat (the flow path connected to the radiator is closed) until the coolant temperature is sufficiently raised in a low-temperature and low-load region.

Therefore, it is possible to maintain the coolant temperature to a high temperature by raising a temperature at which the thermostat is turned on in the low-temperature and low-load region, that is, a temperature at which the flow path connected to the radiator is opened, thereby reducing the time required to warm up the engine and improving fuel efficiency by reducing a frictional loss.

In the case of the electronic thermostat, a method of artificially applying heat through the heating element is applied, such that a speed at which the thermostat is opened and closed is higher than a speed in the case of the mechanical thermostat in the related art, thereby precisely controlling the coolant temperature and effectively preventing overshoot of the coolant temperature.

SUMMARY

The present disclosure provides a control method for engine thermal management which controls operations of an electronic fan clutch and an electronic water pump in cooperation with an operation of an electronic thermostat, thereby achieving efficient engine thermal management and reducing a loss of load.

In one form the present disclosure provides a control method for engine thermal management, the control method including: obtaining an engine coolant temperature and engine driving information; calculating a required fan rotational speed based on the obtained current coolant temperature information and the obtained engine driving information; calculating a control value for controlling a rotational speed of a cooling fan having an electronic fan clutch so that the rotational speed becomes the required fan rotational speed; checking a current operating state of the electronic thermostat; and determining whether to operate the electronic water pump and whether to control the cooling fan rotational speed using the control value, based on the checked current operating state of the electronic thermostat, and controlling the electronic water pump and the electronic fan clutch of the cooling fan based on the determination result.

In one form, when the electronic thermostat is in a closed state after the checking of the current operating state of the electronic thermostat, the electronic water pump may be controlled to be in a slip state.

In another form, fan clutch control for rotating the cooling fan at an idle rotational speed may be carried out in the slip state of the electronic water pump.

In still another form, when the electronic thermostat is in an opened state after the checking of the current operating state of the electronic thermostat, an operation of the electronic water pump may be controlled based on the coolant temperature and the engine driving information.

In yet another form, when the current engine coolant temperature is lower than a predetermined minimum fan operation coolant temperature or the current operating state of the electronic water pump is the slip state in a state in which the operation of the electronic water pump is controlled, fan clutch control for rotating the cooling fan at an idle rotational speed may be carried out.

In still yet another form, when the current coolant temperature is equal to or higher than the minimum fan operation coolant temperature and the current operating state of the electronic water pump is not the slip state in a state in which the operation of the electronic water pump is controlled, the operation of the electronic fan clutch may be controlled in accordance with a control value for controlling the cooling fan so that the rotational speed of the cooling fan becomes the required fan rotational speed.

According to the control method for engine thermal management according to the present disclosure, the operations of the electronic fan clutch and the electronic water pump are controlled in cooperation with the operation of the electronic thermostat, thereby achieving efficient engine thermal management and reducing a loss of load.

It is understood that the term “vehicle” or “vehicular” or other similar terms as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles, e.g., fuel derived from resources other than petroleum. As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example, both gasoline-powered and electric-powered vehicles.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

FIG. 1 is a flowchart illustrating cooperative control logic for an electronic fan clutch and an electronic water pump;

FIG. 2 is a configuration diagram of an engine thermal management system according to the present disclosure; and

FIG. 3 is a flowchart illustrating an engine thermal management control process according to the present disclosure.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

The present disclosure provides a control method for engine thermal management which may achieve efficient engine thermal management and reduce a loss of load by controlling operations of an electronic fan clutch and an electronic water pump (also called a clutch water pump) in cooperation with an operation of an electronic thermostat.

FIG. 2 is a configuration diagram of an engine thermal management system according to the present disclosure and FIG. 3 is a flowchart illustrating an engine thermal management control process according to the present disclosure, which illustrates a cooperative control method for the electronic fan clutch, the electronic water pump, and the electronic thermostat.

One form of the present disclosure, control logic is configured so that an operation of an electronic thermostat 50 may be performed in cooperation with an operating state of an electronic water pump 40 and an operating state of the electronic thermostat 50 may be reflected.

That is, cooperative control logic for an electronic fan clutch and an electronic water pump in the related art is changed, and logic is added to determine whether to operate the electronic water pump 40 depending on an operating state of the electronic thermostat 50 and whether to control a rotational speed of a cooling fan 30 is determined depending on an operating state of the electronic water pump 40.

First, in the control logic for an electronic thermostat 50 an electronic control unit (ECU) 20, may use a three-dimensional map in which an on/off operation region of the electronic thermostat is set depending on a coolant temperature (engine coolant temperature), engine torque (engine load), and based on the operational map, may determine whether to turn on or off the electronic thermostat depending on the coolant temperature detected by a coolant temperature sensor 11 and the engine torque.

Here, it is also possible to use a three-dimensional map in which a vehicle speed condition is added in addition to the coolant temperature and the engine torque, and the operation region of the electronic thermostat 50 is set depending on the coolant temperature, the engine torque, and a vehicle speed determined by a vehicle speed sensor 12, and the vehicle speed condition may be omitted in some cases when the three-dimensional map is applied.

An ON operating state of the electronic thermostat means an OPEN state in which a flow path of a coolant line connected to a radiator is opened as electric power is applied to a heating element, and an OFF state of the electronic thermostat means a state in which electric power is not applied to the heating element and the flow path of the coolant line connected to the radiator is closed.

In the operational map, a thermostat operation region may be set so that the electronic thermostat 50 begins to be turned on under a condition in which the electronic water pump 40 is operated (clutch ON condition), that is, under a condition of the coolant temperature and the engine torque that are lower, by predetermined set values, than a coolant temperature and engine torque at which electric power is applied to a solenoid coil of a clutch in the electronic water pump and a pulley and a pump shaft are connected so that power may be transmitted therebetween.

In the operational map, a thermostat operation region may be set so that the electronic thermostat 50 may be turned off under a condition of the coolant temperature and the engine torque corresponding to a slip region of the electronic water pump 40.

That is, the operational map is set so that the electronic thermostat 50 may be turned on under a condition in which the electronic water pump 40 is operated, the electronic thermostat 50 may be turned off under a condition of the coolant temperature and the engine torque corresponding to the slip region in which the electronic water pump 40 is not operated (an operational signal for turning on the thermostat is not generated when a signal for operating the water pump is not generated).

Of course, logic may be set so that when a signal for operating the electronic water pump 40 is generated by the ECU 20 instead of the operational map, the operational signal for turning on the electronic thermostat 50 is generated in cooperation with the above signal.

As will be described below, the logic is set so that in a state in which the electronic thermostat 50 is turned off, that is, in a state in which the flow path of the coolant line connected to the radiator is closed, the ECU 20 controls the electronic water pump 40 to a slip state.

Here, the slip state of the electronic water pump refers to a clutch off state in which operational electric power is not applied to the solenoid coil of the clutch that is an intermittent mechanism in the water pump and the operational electric power is shut off, a state in which slip occurs between the pulley and a disk, and a state in which the water pump is not operated and control for operating the water pump is not carried out.

In a diesel engine, an operation of the electronic thermostat 50 may be controlled in cooperation with an operating state of a retarder (not illustrated).

In the case of a large-sized diesel engine, a transmission retarder is used to obtain high braking performance, and in this case, heat generated in the retarder is cooled by using an engine coolant.

Therefore, the ECU 20 detects whether a retarder brake is operated, and when the retarder is operated, the thermostat 50 is operated to fully open the flow path connected to the radiator, and the electronic water pump 40 is fully operated at a slip rate of 0%.

In a case in which a condition of the coolant temperature and an engine driving condition correspond to a condition in which the water pump 40 and the thermostat 50 are turned off when the retarder is turned off, the operating states of the thermostat and the water pump are maintained for a predetermined time from a point of time at which the retarder is turned off, and after predetermined time has passed, the thermostat and the water pump are turned off.

When the engine coolant temperature is raised and reaches a predetermined limit temperature, the ECU 20 fully operates the electronic fan clutch of the cooling fan 30, the electronic water pump 40, and the electronic thermostat 50, and fully opens the electronic thermostat 50 when at least one of the electronic fan clutch of the cooling fan 30 and the electronic water pump 40 is abnormally operated.

The basic method of controlling the thermostat has been described above, and a cooperative control method according to the present disclosure will be described with reference to FIG. 3.

As described above, in the present disclosure, the electronic water pump 40 is operated only in a section in which the electronic thermostat 50 is opened, thereby improving an effect of cooling the entire thermal management system and increasing an effect of improving fuel efficiency.

Referring to FIG. 3, first, the ECU 20 obtains a coolant temperature (engine coolant temperature) detected by the coolant temperature sensor 11, and engine driving information including an engine rotational speed (RPM) is detected by the engine rotational speed sensor 13 and engine torque (engine load) (S11).

Next, the ECU 20 calculates a required fan rotational speed based on the obtained current coolant temperature information and the obtained engine driving information.

In this case, the ECU 20 may determine a target coolant temperature based on information on the engine rotational speed and the engine torque (S12), and then may calculate the required fan rotational speed for controlling the coolant temperature to the target coolant temperature based on information on the current coolant temperature obtained by the coolant temperature sensor 11 (S13).

Next, the ECU 20 calculates a control value for controlling the cooling fan 30 so that a rotational speed of the cooling fan 30 becomes the calculated required fan rotational speed.

In this case, the ECU 20 calculates a pulse-width modulation (PWM) value for performing proportional-integral (PI) control so that the rotational speed of the cooling fan 30 becomes the required fan rotational speed by using a cooling fan rotational speed (engine rotational speed x pulley ratio) value obtained from the engine rotational speed and the pulley ratio or the rotational speed value detected by a cooling fan rotational speed sensor 14 as a feedback value (S14).

Here, the PWM value is a control value that is used for the ECU 20 to control an operation of the fan clutch and the rotational speed of the cooling fan 30, and in the following step S20, the ECU 20 outputs a valve control signal for adjusting a valve opening degree of the fan clutch based on the calculated PWM value and controls an operation (valve operation) of the fan clutch (fan clutch PWM control), and performs the PI control so that the cooling fan rotational speed becomes the required fan rotational speed.

Next, after the PWM value is calculated, the ECU 20 checks whether the thermostat is in an opened state, based on information on the current operating state of the electronic thermostat 50, and when the thermostat is in a closed state, that is, when the flow path of the coolant line connected to the radiator is in a closed state, the ECU 20 controls the electronic water pump 40 so that the electronic water pump 40 is in the slip state according to a predetermined slip rate (S17).

When the electronic water pump 40 is controlled to the slip state, fan clutch idle control is carried out (S19), and as a result, the cooling fan is rotated at an idle rotational speed.

In this case, the ECU 20 outputs a valve control signal for rotating the cooling fan 30 at the idle rotational speed, and performs the fan clutch idle control (PWM: 100%).

In contrast, in step S15, when the electronic thermostat 50 is in an opened state, that is, when the flow path of the coolant line connected to the radiator is in an opened state, typical control logic, which controls the operation of the electronic water pump 40 based on information on the coolant temperature and engine driving within a range of slip rate from 0% to 100%, is performed (S16).

Next, in a state in which the operation of the electronic water pump 40 is controlled, it is determined whether the current coolant temperature detected by the coolant temperature sensor 11 is lower than a predetermined minimum fan operation coolant temperature or the current operating state of the electronic water pump 40 is a slip operation state (S18).

In this case, when the current coolant temperature is lower than the predetermined minimum fan operation coolant temperature, or the current operating state of the electronic water pump 40 is the slip operation state, the fan clutch idle control is carried out in order to rotate the cooling fan 30 at the idle rotational speed (S19).

In this case, the ECU 20 outputs the valve control signal for rotating the cooling fan 30 at the idle rotational speed, and performs the fan clutch idle control (PWM: 100%).

In contrast, when the current coolant temperature is equal to or higher than the minimum fan operation coolant temperature and the current operating state of the electronic water pump 40 is not the slip state, the ECU 20 controls the operation (valve operation) of the fan clutch based on the PWM value (PWM: 0 to 100%) for performing the PI control calculated in step S14 so that the rotational speed of the cooling fan 30 becomes the required fan rotational speed (S20).

As described above, whether to control the rotational speed of the cooling fan 30 is determined depending on whether the electronic water pump 40 is operated.

As described above, the cooperative control of the electronic fan clutch, the electronic water pump, and the electronic thermostat is carried out by the ECU as illustrated in FIG. 3, such that it is possible to increase an effect obtained by applying the electronic water pump (an effect of improving fuel efficiency), and since the fan clutch control may be carried out in accordance with the engine driving condition such as the coolant temperature, the engine rotational speed (RPM), and the load (torque), it is possible to reduce a frictional loss by raising the coolant temperature in a low-load region.

The electronic water pump is operated only in a section in which the electronic thermostat is opened, thereby improving an effect of cooling the entire thermal management system and increasing an effect of improving fuel efficiency.

The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure. 

What is claimed is:
 1. A control method for engine thermal management, the control method comprising: obtaining an engine coolant temperature and engine driving information; calculating a required fan rotational speed based on the obtained current coolant temperature information and the obtained engine driving information; calculating a control value for controlling a rotational speed of a cooling fan having an electronic fan clutch so that the rotational speed becomes the required fan rotational speed; checking a current operating state of an electronic thermostat; and determining whether to operate an electronic water pump and whether to control the cooling fan rotational speed using the control value based on the checked current operating state of the electronic thermostat, and controlling the electronic water pump and the electronic fan clutch of the cooling fan based on the determination result.
 2. The control method of claim 1, wherein when the electronic thermostat is in a closed state after the checking of the current operating state of the electronic thermostat, the electronic water pump is controlled to be in a slip state.
 3. The control method of claim 2, wherein fan clutch control for rotating the cooling fan at an idle rotational speed is carried out in the slip state of the electronic water pump.
 4. The control method of claim 1, wherein when the electronic thermostat is in an opened state after the checking of the current operating state of the electronic thermostat, an operation of the electronic water pump is controlled based on the coolant temperature and the engine driving information.
 5. The control method of claim 4, wherein when the current engine coolant temperature is lower than a predetermined minimum fan operation coolant temperature or the current operating state of the electronic water pump is in a state in which the operation of the electronic water pump is controlled to be in a slip state, fan clutch control for rotating the cooling fan at an idle rotational speed is carried out.
 6. The control method of claim 4, wherein when the current coolant temperature is equal to or higher than a minimum fan operation coolant temperature and the current operating state of the electronic water pump is in a state in which the operation of the electronic water pump is controlled to not be in a slip state, the operation of the electronic fan clutch is controlled in accordance with a control value for controlling the cooling fan so that the rotational speed of the cooling fan becomes the required fan rotational speed.
 7. The control method of claim 1, wherein the electronic thermostat is controlled based on the current engine coolant temperature and engine torque by using a map in which opening/closing operation regions are set in accordance with the engine coolant temperature and the engine torque.
 8. The control method of claim 7, wherein the operation region is set in the map so that an operation of opening the electronic thermostat is carried out under a condition of the engine coolant temperature and the engine torque that are lower, by predetermined set values, than an engine coolant temperature and engine torque at which the electronic water pump is operated.
 9. The control method of claim 1, wherein the electronic thermostat is controlled based on the current engine coolant temperature, engine torque, and a vehicle speed by using a map in which opening/closing operation regions are set in accordance with the engine coolant temperature, the engine torque, and the vehicle speed.
 10. The control method of claim 9, wherein the operation region is set in the map so that an operation of opening the electronic thermostat is carried out under a condition of the engine coolant temperature and the engine torque that are lower, by predetermined set values, than an engine coolant temperature and engine torque at which the electronic water pump is operated.
 11. The control method of claim 1, wherein an operation of the electronic water pump and an operation of the electronic thermostat are carried out in cooperation with each other, such that the electronic thermostat is controlled to an opened state when the electronic water pump is operated, and the electronic thermostat is controlled to a closed state when the electronic water pump is in a slip state.
 12. The control method of claim 1, wherein operations of the electronic thermostat and the electronic water pump are carried out in cooperation with an operation of a retarder, such that when the retarder is operated, the electronic thermostat is controlled to an opened state, and the electronic water pump is fully operated to a state of a slip rate of 0%.
 13. The control method of claim 1, wherein operations of the electronic thermostat and the electronic water pump are carried out in cooperation with an operation of a retarder, such that when a condition of the engine coolant temperature and an engine driving condition correspond to a condition in which the electronic thermostat is closed and the electronic water pump is turned off at a point of time at which the retarder is turned off, the opened state of the electronic thermostat and the operating state of the electronic water pump are maintained for a predetermined time from a point of time at which the retarder is turned off, and after the predetermined time has passed, the electronic thermostat is controlled to be closed and the water pump is controlled to be turned off.
 14. The control method of claim 1, wherein the electronic thermostat is controlled to be fully opened when at least one of the electronic fan clutch of the cooling fan and the electronic water pump is abnormally operated. 